Liquid percussion motor

ABSTRACT

A FLUID ACTUATED TOOL FOR APPLYING REPEATED PRECUSSIVE BLOWS TOA DRILL BIT IN TYHE DRILLING OF OIL AND GAS WELLS IS DISCLOSED. IN PARTICULAR, THE INVENTION CONCERNS PERCUSSION MOTOR FOR INCORPORATION IN DRILL STRINGS, CAUSING DRILL BITS TO VIBRATE OR OSCILLATE AXIALLY AT THE SAME TIME THEY ARE BEING ROTATED FOR THE DRILLING OF SUCH WELLS. THE DISCLOSURE INCLUDES A PERCUSSION MOTOR CONTAINING TWO MOVING PARTS, A STEPPED PISTON-TYPE HAMMER AND A CENTRAL CYLINDRICAL VALVE ASSEMBLY. THE STEPPED PISTON-TYPE HAMMER IS ARRANGED IN A MATING STEP-TYPE HOUSING. AN ANVIL IS SLIDEABLY MOUNTED WITHIN THE HOUSING BELOW THE HAMMER AND ARRANGED FOR ONLY LIMITED AXIAL MOVEMENT, AND ARRANGED TO BE STRUCK BY THE HAMMER. THE CENTRAL VALVE ASSEMBLY COOPERATES WITH PARTS OF THE HAMMER AND FLOWING FLUID AND THUS OSCILLATES BETWEEN AN UPPER SEAT IN THE LOWER PART OF THE HAMMER AND A LOWER SEAT IN THE TOP ANVIL. THIS VALVE OSCILLATION IN TURN APPLIES A RESULTANT FORCE ALTERNATIVELY TO THE TOP AND BOTTOM OF THE SLIDEABLY MOUNNTED HAMMER, CAUSING IT TO OSCILLATE AXIALLY. IN A PREFERRED EMBODIMENT, MEANS ARE PROVIDED TO DAMPEN THE UPPER END OF THE VALVE MOTION. VARIOUS EMBODIMENTS OF THE INVENTION ARE DESCRIBED.

July 18, 1972 R. P. VINCENT ETAL Re. 27,434

LIQUID PERCUSSION MOTOR Original Filed 001;. 24, 1966 5 Sheets-Sheet l lSI 64 E 29 F|G.6

INVENTORS: RENIC P. VINCENT WRENCE B. WILDER ATTORNEY July 18, 1972 R.P. VINCENT ETAL LIQUID PERCUSSION MOTOR Original Filed Oct. 24, 1966 5Sheets-Sheet 3 FIG.5

7/7 W y w/ INVENTORS RENIC P. VINCENT BY LAWRENCE B. WILDER ,QMQ MATTORNEY July 18, 1972 VINCENT ET AL Re; 27,434

LIQUID PERGUSSION MOTOR iled Oct. 24, 1966 5 Sheets-Sheet 4 OriginalINVENTORSZ RENIC P. VINCENT LAWRENCE B. WILDER ATTORNEY July 18, 1972 pvmc ETAL Re. 27,434

LIQUID PERCUSSION MOTOR Original Filed Oct. 24, 1966 5 Sheets-Sheet 5 60 4 J ii KYYxiV/ W 7/ 7// 7/// I! Ill VV/ m.\\\ \&%//

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INVENTORS: RENIC' P. VINCENT wAWRENCE B.WILDER ATTORNEY United StatesPatent 27,434 LIQUID PERCUSSION MOTOR Renic P. Vincent and Lawrence B.Wilder, 'Ihlsa, Okla, assignors to Pan American Petroleum Corporation,Tulsa, Okla.

Original No. 3,327,790, dated June 27, 1967, Ser. No. 596,374, Oct. 24,1966. Application for reissue Sept. 13, 1968, Ser. No. 767,534

Int. Cl. B25d 17/06 U.S. Cl. 173-73 30 Claims Matter enclosed in heavybrackets appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade bv reissue.

ABSTRACT OF THE DISCLOSURE A fluid actuated tool for applying repeatedprecussive blows to a drill bit in the drilling of oil and gas wells isdisclosed. In particular, the invention concerns percussion motor forincorporation in drill strings, causing drill bits to vibrate oroscillate axially at the same time they are being rotated for thedrilling of such wells. The disclosure includes a percussion motorcontaining two moving parts, a stepped piston-type hammer and a centralcylindrical valve assembly. The stepped piston-type hammer is arrangedin a mating step-type housing. An anvil is slideably mounted within thehousing below the hammer and arranged for only limited axial movement,and arranged to be struck by the hammer. The central valve assemblycooperates with parts of the hammer and flowing fluid and thusoscillates between an upper seat in the lower part of the hammer and alower seat in the top of the anvil. This valve oscillation in turnapplies a resultant force alter natively to the top and bottom of theslidealbly mounted hammer, causing it to oscillate axially. In apreferred embodiment, means are provided to dampen the upper end of thevalve moition. Various embodiments of the invention are described.

This application is a continuation-in-part of co-pending application404,046, entitled, Liquid Percussion Motor, filed Oct. 15, 1964, nowabandoned, Renic P. Vincent and Lawrence B. Wilder, inventors.

This invention relates to fluid-actuated tools for applying repeatedpercussive blows to a drill bit in the drilling of oil and gas wells,and the like. In particular, the invention concerns percussion motorsfor incorporation in drill strings, permitting drill bits to vibrate oroscillate axially at the same time that they are being rotated for thedrilling of such wells.

A number of designs of such percussion motors have been suggested in thepast. Those which have had a measure of success in practice have beendesigned for use with a stream of high-pressure gas such as compressedair, or natural gas. The percussion motor is mounted at the lower end ofthe drill string and, in turn, is connected at the bottom to a suitabledrilling bit. The stream of highpressure gas, circulating through thedrill string, percussion motor and bit, causes the bit to oscillatepercussively against the formation and, thus, produces a major part ofthe drilling effect. The drill string is customarily rotated both toproduce further drilling effect and to minimize deviations in thedirection of the hole. The flow of air up the annulus between the wallsof the hole and the drill string carry the formation cuttings and Wellfluids to the surface.

Such equipment does not work well when it is necessary to use a liquid(customarily a water or an oil base drilling fluid) to control flows ofwell fluids into the well and to carry formation cuttings to thesurface. It is well known Reissued July 18, 1972 ice that the hydroulichead imposed by the annular column of liquid olfers control undersubstantially all conditions against undesired flow of formation fluidsinto the bore.

However, since the specific gravity of liquid drilling fluids is manytimes that of gaseous drilling fluids and elastic properties aregenerally much lower, up to the present it has not been found possibleto operate percussion motors satisfactorily in commercial drilling,using liquids as the actuating fluid. It must be kept in mind thatrotary-percussive drilling is uneconomical unless the bit can be kept onbottom and drilling for long periods of time. The percussion motor must,therefore, be very rugged to permit commercial operations.

Even through drilling liquids returning to the surface usually passthrough vibrating screens and are circulated through settling zones inthe mud pits, it is substantially impossible to produce a stream ofmaterial to be recirculated through the drill string which contains noquantity of abrasive solids. Accordingly, it is very definite problem inthe design of liquid-actuated percussive drilling motors to be able tomaintain valve operation without excessive abrasion and resultant wear.Ordinarily, this is a problem with all moving parts in the motor.

It is also necessary to minimize effects of water hamper. Percusionmotor valves must close rapidly to be effective. The frequently resultsin the formation of shock waves in the liquid, which may causemisoperation or destructive stressing of the motor parts.

It is an object of the present invention to provide a liquid-actuatedpercussion motor satisfactory for effective field operation in thedrilling of oil, gas and water wells, and the like. A further object ofthe invention is to provide such a motor which may additionally beactuated by gas, if desired. A further object is to provide such a motorwhich can be operated at high frequency (of the order of 3,000 blows perminute, or more). \Another object is to provide a percussion motorcontaining a minimum of moving parts, and in which possible breaking orabrasion of the motor parts is minimized. Another object is to providesuch a motor in which water hammer is not a major problem. Still anotherobject is to provide a percussion motor sufficiently independent ofgravitational effects to be usable horizontally or oriented upwards.Further objectives and purposes of the invention will become apparent byperusal of this specification.

The invention is illustrated by the accompanying drawings which form apart of this specification. In these drawings:

FIGURE 1 is a diagrammatic cross section of one form of the percussionmotor.

FIGURE 2 is a cross section of one complete form of such a device.

FIGURES 3 to 5 show an enlarged cross section of a portion of the motorillustrated in FIGURE 2, during different parts of an operating cycle.

FIGURE 6 shows a detail of a part of the valve assembly shown in FIGURES2 through 5.

FIGURES 7 to 11 are diagrammatic cross sections of still furtherombidiments of this invention.

In the drawings the same reference number refers to an identical orcorresponding part.

In all of these designs the percussion motor basically contains twomoving parts, a stepped piston-type hammer, and a central cylindricalvalve assembly. There is a casing, or housing, to confine the actuatingfluid, and an anvil slidea'bly mounted within the casing below thehammer, but arranged for only limited axial motion. This anvil in turnis connected directly, or remotely, to the drilling bit. The anviladditionally is provided with splines and projections meeting withsimilar splines and projections in the inside lower part of the casingso that axial orque applied from the drill string to the casing willreate the drilling bit while percussive drilling is proceeding.

In operation, the percussion motor is mounted at the ottorn of a drillstring, or string of pipe, which is rotataly mounted in a drill rig andsupplied with a high-presure fluid. Ordinarily this will be a liquid,though gas may be used. This fluid does work in passing through theibratory drilling device, or percussion drilling tool, exeriencing adrop in pressure and being exhausted from n exhaust passageway in thedrill bit affixed to the anvil 'f the percussion motor. The drillingfluid at lower presure then returns to the surface, removing the drillcutings in its passage.

The central valve assembly oscillates between an upper nd lower positionwhich in turn applies a resultant force lternately to the top and bottomof the slideably mounted .ammer, causing it to oscillate axially. Aftereach upward ycle of the hammer it is impelled forcibly downward impacton the anvil, thus in turn causing the anvil to pply a series ofpercussive blows to the drill bit in conact with the earth formations.Preferably the drill string i rotated by the drill rig during this timeso that between lows' the drill bit is rotationally indexed to strike alightly different part of the formation.

In FIGURE 1 the tubular casing 11 is attached by ieans (not shown) tothe lower end of a conventional vrill string, as already described. Itis essential that this lbular casing 11 includes an upper portion ofsmaller aside diameter than that of the lower portion of this aember.Such relationship is shown in FIGURE 1. It is lso essential that thereis a radial port 12, that is, a hole hrough the wall of this casingbelow the junction 13 of he upper and lower portion but near thisjunction.

Th'e' hollow stepped cylindrical hammer 14 is mounted or axial slidingwithin casing 11. The upper outer diamter of hammer 14 is machined tofit closely in the upper :ortion of casing 11. Similarly, the lowerouter diameter f hammer 14 closely fits the adjacent lower portion ofasing 11. Resilient seals 15 and 16 are preferably em- |loyed, eithermounted on the casing 11 and in contact vith the hammer 14 or mounted onthe outer diameter of he hammer 14 and in contact with casing 11. It isto be lnderstood that the hammer is arranged for minimal eakage of fluidfrom the hollow bore 40 of casing 11 to torts 12. However, this does notdemand that the entire Iuter diameter of either section of the steppedhammer .4 need be of uniform diameter. Only that portion which employedto seal off liquid flow need be a maximtun liameter; the rest may berelieved or of slightly less outer liameter, to minimize friction.

A center tube 17 is provided for use in controllmg movement of the valveassembly. Center tube 17 1S prefrably a thin walled pipe of uniformdiameter concenrically mounted in casing 11 with the upper end 18comnunicating directly with the outside of casing 11 A valve assemblyessentially consisting of a piston 19, .n axially symmetric valveelement 20, and a coimectmg od 21 for communicating force between piston19 and 'alve element 20 is mounted substantially axially withthe iiStOll19 closely fitting the inside of tube 17. There is a lownward force onthe upper face of piston 19 due to the Iressure of the fluid immediatelyoutside casing 11 1m- !osed. through the opening 18 and tube 17 on thistop sur- Face of piston 19. There is a greater upward force on the)ottoln face of this piston 19. Basically this greater upvard force isdue to the fact the upward pressure on the iottom of piston 19 is thepressure of the operating liquid n the bore 40 of casing 11 which is ata considerably iigher pressure than that outside casing 11, customarilynore than 100 p.s.i. greater.

The cylindrical valve element 20 includes carefully nactliued lower andupper surfaces 22 and 23 respectively. Near the bottom of the steppedhammer 14 the bore of :he hammer is decreased and an annular member 24is Jrovided with an upper valve seat for the upper surface 23 of valveelement 20. A lower seat 25 for the lower surface 22 of valve element isprovided in a recess in the top of the hollow cylindrical anvil 26. Thisanvil is slideably fixed within casing 11 below the hammer 14. Since itis desirable to have the exhaust liquid vented through the hollow bore27 of anvil 26 only, preferably resilient seal 28 is mounted either onthe inner diameter of the casing 11 and touching the upper part of theanvil 26, or on the upper outer diameter of anvil 26 and touching casing11. If seals 28 are used, then it is desirable to include a passageway28A from the top of the anvil, through the body of the anvil topassageway 27 below seat 22 to make the tool easier to start. The bottompart of the anvil 26 is arranged relative to the casing so that torquecan be transmitted from casing to anvil as is shown in FIGURE 2.

A partition 29 is employed inside of the central tube 17 and outside theconnecting rod 21 of the valve assembly. This seals between the tube 17and the rod 21 so that fluid pressure below this means is nottransmitted to the inside of the central tube above the partition. Thispartition 29 may be mounted on the tube 17 and in sealing relationshipto the rod 21, as shown in FIGURE 1 or mounted stationary with respectto the hammer 14 and in sliding sealing relationship to the tube 17, asis shown in later figures.

When this tool is mounted on the end of the drill string, with the drillbit resting on the formation to be drilled and connected to anvil 26,and a supply of pressure fluid, preferably liquid, present in bore 40,the valve assembly and the hammer 14 oscillate axially alternately tocause the bottom face 30 of the stepped hammer 14 toimpact and transfermuch of its momentum to the top face 31 of the anvil 26, thus repeatedlypercussing the attached drill bit against the face of the formation.

The operation involves one additional element-an annular valving elementwhich is FIGURE 1 is an annular projection 32 on the inner bore of thestepped hammer 14, carried by said hammer above annular member 24. Thisannular member 32 is shaped so that as hammer 14 moves upward theannular member will slideably fit around center tube 17 and reduceconsiderably fluid communication from bore 17 to bore 33. Thus, in thepart of the cycle illustrated in FIGURE 1, with the cylindrical valveelement 20 seated on seat in anvil 26, the upward force on the lowerface of hammer 14 is greater than the downward force on the upper face34 of the hammer (due to the stepped construction) so the hammer movesupward under the pressure of the liquid in bore 17. However, as soon asthe annular member 32 is adjacent the lower end of center tube 17, itreduces the fluid flow into bore 33. This reduction in fluid flow isaccompanied by a substantial decrease in pressure in bore 35 so thatultimately as hammer 14 moves upward, the hydraulic force exerted on thetop 34 of hammer 14 exceeds the upward force exerted by the liquid onthe bottom face 30 of this hammer. At about the same time, the downwardforce exerted on the valve element 20 (the difference of pressure inbore 35 and that in passageway 27 times the cross sectional area of thevalve seat 25) decreases. The upward force on the bottom face of piston19 will be essentially that in bore due to port 36 in tube 17, and thisforce will tend to increase as the annular member 32 cuts off, orreduces, flows of fluid to bore 33. The increase in upward force onpiston 19 lifts the valve assembly from the lower seat 25 and propels itrapidly in an upward direction. We prefer that near the upper end of itsstroke the valve motion be damped. This can be accompanied in variousways which are shown in the several figures. Thus, in FIGURE 1 the valveseat 24 is recessed into the stepped hammer 14. Below this seat, thebore of the hammer is slightly larger than the maximum diameter of thevalve element 20 so that when moving up relative to the hammer and nearthe seat 24, the valve element 20 will produce considerable eddying inthe liquid and hence damp the strik- L ing of the upper surface 23 ofvalve element on its upper seat in member 24.

Now the fluid-filled volume below the seat in member 24 is incommunication with the exhaust passageway 27 in the anvil 26, and thepressure within this space rapidly decreases. The downward force due tothe pressure of th! liquid on the upper face 34 of stepped piston 14rapidly propels it downward. There is still a net upward force on thevalve assembly composed of parts 19, 20 and 21 and therefore cylindricalvalve element 20 remains seated against the seat in member 24 during thedownward movement of hammer 14. This requires that the net upward forceagainst the piston 19 (the pressure at part 36 times the area of piston19 less the area of stem 21 opposed by the pressure in chamber 55 timesthe area of piston 19), be greated than the net downward force on valveelement 23 seated in member 24 (the pressure in chamber 33 times thearea of the minimum diameter of the upper valve seat in member 24 lessthe area of the stem 21 opposed by the pressure in chamber 35 times theminimum seat area in element 24). A convenient way to obtain the propernet force is to make the inside diameter of tube 17 greater than theminimum diameter of the upper valve seat in member 24.

The hammer 14 comes down to and impacts on the top face 31 of the anvil26. It is important that there be no restriction in motion of the hammerjust as it is about to strike the anvil. Accordingly, it is desirable,though not essential, to provide at least approximately radial groovesin either the upper face 31 of anvil 26 or the lower face 20 of hammer14, or both, so that remaining liquid between these faces can be ejectedrapidly into the exhaust passageway 27. This permits maximum impulseduring the transfer of momentum from stepped hammer 14 to anvil 26.

During the downward motion of stepped hammer 14 the annular valve member32 has once more cleared the end of the central tube 17, thus increasingpressure in bore 33 and consequently the downward pressure on the valveasembly. However, this pressure is not suffiient to unseat the valve. Atthe instant of impact, however, there is a maximum downward accelerationdue to the abrupt stopping of hammer 14. Since the valve assemblycontains considerable inertia, there will be an additional downwardforce at impact (not before) which is the product of the inertia timesthe acceleration. This furnishes the major downward force at thisinstant on the valve assembly. It is sufficient to unseat the valve fromits upper position against seat 24 and to propel it quite rapidly intothe lower seating position shown in FIGURE 1, in which the lower face 22is in contact with seat 25. Before valve 20 is unseated from seat 24,there is an area A, exposed to the pressure of fluid in bore 33;however, when the valve is unseated there is a larger area A exposed tothe pressure in bore 33. The enlarged exposed area aids in driving thevalve 20 downward. The sealing area of seat has a diameter which exceedsthe diameter of piston 19. Since the pressure in passageway 27 isapproximately the same as that in the upper section 55 of tube 17 (thereis no flow between these passages at this time), and since the pressurein bore 35 is now substantially the same as that on the lower srface ofpiston 19, it follows that there is a net seating pressure on the valveassembly tending to hold it against seat 25 in anvil 26 until theannular valve element 32 again minimizes flow into bore 33. In themeantime the pressure in bore 35 assumes a value somewhat less than theworking pressure of the fluid in bore (due to drop through theintervening passages), but there is a net upward force on the hammer 14causing it to start the next cycle.

Preferably valve seat 25 is recessed into the upper part of anvil 26sufliciently so that the maximum diameter of the cylindrical valveelement 20 can be accommodated below the top face 31 of anvil 26. Thevalve seat 25, and the recess above it, are aligned with valve element20 and valve element 20 closely fits this recess. Accordingly, if at anypart in the cycle when valve element 20 should be seated on seat 25 itleaves this seat, the pressure on the upper face 23 of this valve willgreatly exceed that on the bottom surface (which will be substantiallyequal to the pressure in exhaust passageway 27) and the valve willimmediately re-seat.

One major difliculty which has been experienced with percussion drillingmotors in the past is that their valves have been exposed to repeatedhigh stresses and, therefore, break rapidly. This effect is minimized inthe percussion drilling motor, or vibratory drilling device, formingthis invention. It has seen that the forces are applied hydraulicallyand it is also seen that the design inherently provides for dam-ping atthe end of the valve upstroke. It is further seen, by an inspection ofFIGURE 1 (and later in FIGURE 6), that the valve element and itsconnection to the piston 19 are arranged to minimize stress by havingmaximum radii of curvature from the connecting rod 21 to both the valveelement 20 and the piston 19. No springs (devices inherently subject tobreakage) are used. Also, there is no dependence on the force of gravityin the working of the device.

A drawing of a complete drilling device made in accordance with ourinvention is shown in FIGURE 2. Here the casing 11 is fitted at theupper end with a threaded section 37 suitable for connection to thedrill string (not shown). In turn, the member 11 is threadably connectedto member 11a, which is an extension of this casing of greater internaldiameter than that of the upper section. The upper end of center tube17, which is concentrically mounted within the casing. contains amounting head 38 containing a passageway 39 which connects the bore 40with the passageway 41 outside tube 17 and within the hammer 14.Preferably the cross sectional area of passage 39 is made as great aspossible to minimize pressure drop. The stepped piston hammer 14 ismounted within the casing 11 as already discussed in connection withFIGURE 1. Ports 12 in casing 11 are sized to minimize pressure effectsotherwise present in the variable volume between the stepped casing andthe stepped hammer due to reciprocation of this hammer. Most of themajor outer diameter of hammer 14 is slightly less than the innerdiameter of lower portion 11a of casing 11, to permit axial motion ofthe hammer with minimal friction. Lower section 14a is screwed into thestepped hammer 14. Its outer diameter closely fits that of the lowersection 11a of the casing and the resilient seal 16 insures that thereis a minimum fluid leakage past the hammer. The top surface of thehammer 14 is shown beveled, which is advantageous to deflect the flow ofthe working fluid into pas sageway 41.

One preferred form of anvil 26 is shown in FIGURE 2. It is hollow andincludes passageway 27 as before. At the lower end, anvil 26 is providedwith means for transmitting torque from the casing 11 to the drill bit.Many variations of such torque transmission arrangements have been shown(for example, that described in US. Letters Patent 3,101,796). There isno particular functional difference in the many variations that can beemployed; some are more easily made than others. In the arrangementshown in FIGURE 2, the lowermost part of the casing 11a has a decreasedinside diameter consisting of a plurality of axial ridges 44, betweeneach two of which are splines or grooves. These ridges 44 engageequivalent splines or grooves cut into the outer diameter of the lowerportion of the anvil 26. In between these splines in anvil 26 are raisedportions 43 which mate with the corresponding splines in the enlargedportion of casing 11a. A sub 45 is screwed on to the lower end of anvil26. In drilling position it butts against casing 11a, since its outerdiameter is substantially that of the portion of this casing 11. Thesplines in both the anvil 26 and the casing 11a are longer than thecorresponding or mating ridges, so that until the drill bit touchesbottom there is a vertical distance that 7 nvil 26 can move between theposition shown in FIG- JRE 2 and a lower position in which adjacentsplines nd ridges are in top contact. This arrangement is referred o inthe claims by stating that the anvil is slideably Lxed within thecasing. That is, it has a limited amount If axial motion between stops.

The sub 45 is provided at the lower end with a threaded ection 46 sothat a drill bit can be threadably connected lirectly to the anvil. Thefluid passageway 27 through the hollow anvil extends through the sub.Since drill bits are nanufactured with an axial passageway, there iscomplete luid communication from bore 40 through the anvil and lrillbit. The amount of axial travel permitted by the plined arrangementbetween anvil 26 and the casing 11a made suflicient so that when thedrill bit is not in conact with the formation, the piston 19 is belowthe ports 6. This position results because the pressure acting on hevalve keeps the valve 20 in the bottom of the hammer losed and thehammer will continue to move downward lntil the piston 19 clears ports36. At this time the direcion of the force on the valve changes to openthe cloure in the bottom of the hammer. The hammer then will issume someintermediate position in which fluid is circuated from inside the pipeto the well annulus through both he anvil passageway 27 and through thetube 17 and out utlet 18. This permits free circulation of fluid at anytime he anvil 26 is fully extended.

It also provides a means for starting the hammer to scillate. It hasalready been shown that inertial forces It the valve member resultingfrom stopping the downvard motion of the hammer are necessary todislodge the alve from the hammer seat. It follows that when the 001cannot be started when the anvil is not extended, the warmer is incontact with the anvil and the hammer valve 5 closed.

Actual starting occurs as follows: As the anvil 26 moves lpward due tothe bit contacting the formation and as he drill pipe is lowered, thehammer 1-4 which is floating ome distance above the anvil moves upwarduntil the )iS'tOIl 19 crosses the ports 36. This shuts off the flowhrough tube 17, producing an upward force on the valve lssembly whichcloses the valve against the seat in memer 24. This causes the hammer 14to move downward rntil the hammer 14 strikes the anvil 26. Since theanvil las not as yet traveled upward to its normal operating aosition,the hammer makes a longer than normal stroke and strikes the anvil. Thevalve moves from its seat in the iammer to that in the anvil. With theanvil valve closed, he hammer moves upward and is reversed in a normalnanner. Thus it can be seen that as the anvil moves upward to its normaloperating position the hammer stroke lecreases and the frequencyincreases until normal condiions are obtained.

The arrangement of the annular valve member 32 is :lightly different inFIGURES 2 to 5 from the arrangenent shown in FIGURE 1. In these figures,this element Yorms part of a sleeve 47 which is concentrically mountedwithin the lower hammer member i14a by means of a :pacer washer 48 andstop 49. Above element 32, the ileeve 47 is hollowed to provide apassageway 50. The ninimum diameter of valve element 32 is slightlygreater ban the outside diameter of the center tube 17, so that when 32approaches the lower end of center tube 17, as thOWIl in FIGURE 4, theflow of fluid is considerably reluced and preferably is substantiallyshut off.

Sleeve 47 contains a plurality of webs 51 between which there are fluidpassages (shown by the dotted lines n FIGU RES 2 to 5) to permit fluidflow past the webs. [he webs, in turn, support a valve rod guide 52which llll'I'OllIldS rod 21 and maintains it substantially coaxial. Theupper part of rod guide 52 is extended into a piston 53 which closelyfits the inside diameter of center tube [7 and effectively minimizesfluid flow from the lower and of this tube. Accordingly, piston 53 formsa partition :losely fitting the rod 21 and tube 17 and is attached tohammer part 14a. The liquid in cavity 54 (communicating through ports 36with passageway 41) exerts only an upward force through the bottom ofpiston 19 on the valve assembly. The fluid pressure in bore 55 abovepiston 19 is equal to the pressure in the opening 18 of casing 11 andis, therefore, considerably lower, so that a net resultant upward forceis present, tending to unseat the cylindrical valve element 20 from seat25 in anvil 26.

However, as stated earlier, the sealing area of seat 25 has a diameterwhich exceeds the inside diameter of tube 17 or the outer diameter ofpiston 19 (substantially the same). When, as in FIGURE 3, the valveelement 20 is seated on seat 25, the pressure of the liquid in bore 35maintains the valve assembly seated as earlier mentioned, the recess 56which, like seat 25, is aligned with a valve assembly, is made justslightly larger than the maximum diameter of the valve element 20. Thus,if the valve element 20 is temporarily unseated from seat 25 while thefluid working pressure still exists in bore 35, the unseating force dueto the pressure on the bottom side of valve 20 is much less that theseating pressure on the top side and the valve immediately returns toits seated position until a substantial upward force is imparted to thevalve assembly.

With the valve assembly in its lowermost position, the fluid pressureexerted through passageway 4-1 on bore 35 is exerted against the bottomface 30 of the hammer 14 and the hammer 14 rises, as shown in FIGURE 4.

When annular valve member 32 approaches the bottom of center tube 17,fluid communication between passageway 41 and bore 35 is reduced and thepressure in bore 35 decreases rapidly as the volume of bore 35 increasesdue to upward hammer movement. This imparts a strong upward force to thevalve assembly, which unseats it. Force on the valve element 20 nowsubstantially balances out and the net upward force, due to the highpressure in cavity 54 and the low pressure in bore 55, rapidly moves thevalve assembly to the upper position.

As shown most clearly in FIGURES 3 to 5, the annular upper valve seatingmember 24 in this case is slideably fixed within hammer 1-4, that is,member 24 has limited axial motion between the stop consisting of thelower face of sleeve 47 and a second stop 57 in the inner wall of hammer14 but above face 30. When the valve assembly is in the lowermostposition closing passageway 27, the annular member 24 tends to rideagainst the lower stop 57. Thus, the space between the top of thismember and the bottom of sleeve 47 is filled with liquid. When, as shownin FIGURE 5, the valve assembly is sharply drawn up against the seat ofannular member 24 the liquid above this member is forced into bore 35.

It is desirable, though not essential, that annular member 24 be locatedsufiiciently above the bottom face 30 of hammer 14 so that the valveelement 20 may be recessed within the hammer, as shown in FIGURE 5,preferably with relative small clearance between the maximum diameter ofthe valve element and the minimum diameter of the recess 58 in thehammer. This increases the dashpot action; it also provides that whenvalve element 20 leaves the upper seat, any tendency of valve element 20to reclose is minimized since the downward hydraulic force on the upper,larger face of valve element 20' is effective. This also adds to theinertial force effective in moving the valve element 20 from the upperseat to the anvil seat 25. It has been earlier specified that it is essential that the minimum area of the seal in annular member 24 be lessthan the area of piston 19 or tube 17.

In the arrangement shown in FIGURES 3 to 5, the length of stroke of thehammer is essentially governed by the maximum distance between the upperedge of annular valve member 32 and the lower edge of tube 17, since assoon as the fluid flow into bore 35 is minimized, the major force on thehammer is in a downward direction; the hammer is rapidly decelerated toa complete stop and accelerated in a downward direction. This downwardmotion continues until the hammer seats by impact against anvil 26, asshown in FIGURE 3. Any liquid present between the hammer and anvilexhausts through the center hollow part of exhaust passageway 27. To aidin the final drainage, at least substantially radial grooves 59 are cutin either the hammer or anvil. g

iPreferably, but not essentially, the central part of the valve assemblyis made hollow by passageway 60. This simply insures that the relativelylow pressures in bore 27 and bore 55 are substantially equal most of thetime. The bore is sufficiently small so that the impedance to flow ofliquid through this passageway is large and, accordingly, there islittle leakage.

It is noted that in FIGURES 3 to 5 the outer diameter of the hammer isrelieved at the bottom, and in the upper part above the area where theresilient seal 16 may contact the hammer 14. Diameter increase due topeening can be alleviated by relieving the outer diameter of the hammer14 just above the lower face 30 and the outer diameter of the anvilbelow its upper face 31 without aifecting the clearances between case11a and 14a and the mating surfaces on the hammer and anvil.

It should be noted, as mentioned above, that the valve assemblypossesses considerable inertia. The inertia force resulting when hammer14 strikes anvil 26 furnishes the major downward force unseating thevalve assembly from its uppermost seating position, shown in FIGURE 5,to its lowermost seating position, shown in FIG. 3. This is verydesirable since it substantially prevents the opening of the valveduring the downward stroke and thus minimizes a chance of impededdownward motion of the hammer 14 against the anvil 26. This is a specialfeature of this design of very definite importance.

It is aparent that the valve assembly arrangement, shown in the enlargedviews of FIGURES 3 through 5, is essentially diagrammatic. Two points ofexplanation need be made. The sleeve 47 preferably is made of twomatching split halves separated by a co-axial central plane, so that theguide may be placed around rod 21 during assembly. We have also found itdesirable to make the piston 19 as shown in cross section FIGURE 6. Theupper part of the rod 21 is threaded. Screwed to it are lower ring 61and upper ring 62 which are jammed together. Between these is a groovecontaining resilient seal 63 which tends to seal between the piston 19and the center tube 17. The radii of curvature at 64 where theconnecting rod and piston meet, and the corresponding radius ofcurvature where the rod widens into the valve element 20, are as largeas possible, to minimize the stress at these filleting points.

As an example of the effectiveness of this design, test models of a toolbuilt substantially in accordance with the design of FIGURE 2, but withabrupt curves and no damping provisions, showed valve assembly failuresafter operating periods of a few score minutes at most. The design shownin FIGURES 3 to 5 was set up as a demonstration with a valve assemblymade of aluminum alloy rather than steel (which, of course, would beused in practice) and successful operation for 9 hours was obtained.Operation without failure for over 41 hours was obtained using steelvalves.

FIGURE 7 shows diagrammatically a rotary percussion drilling tool of thetype already discussed. However, in this case, the minimum diameter ofhammer 14 opposite the center tube 17 has been locally decreased to makea substantially sliding fit at 65. An O-ring seal 66 has been added. Inthis case, therefore, fluid flow is through passageway 41 and ports 36and out the bottom of tube 17. The annular valve member in this case is,a member 67 mounted in the hammer 14 with a piston-like top member 68with maximum diameter slightly less than the inner diameter of tube 17;This piston is so located that when hammer 14 reaches substantially thetop of its stroke, piston 68 enters tube 17 and thus minimizes or shutsoff flow of liquid from passageway 41 into bore 35.

Axial passageways 69 are provided in annular member 67 to permit flowfrom passageway 41 to bore 35 except when piston 68 is at least adjacenttube 17.

In FIGURE 8 a different system, still in accordance with our invention,is used to impart an upward axial force to the valve assembly to unseatvalve element 20. In this case there is no lower radial port in thecenter tube 17 and piston 19 is always subjected to the difference inforce due to pressures in bore 55 and in passageway 41. This, ispreviously discussed, is always an up ward force. However, since thesealing. area of lower seat 25 of the valve element 20 exceeds the crosssectional area of the interior of tube 17, an upward unseating force isnecessary to initiate motion of the valve element from its lower toupper position. In this case this is achieved by mounting on hammer 14an impact means consisting of plate 70 containing axial fluidpassageways 71 for permitting flow from passageway 41 to bore 35. Thisplate 70 surrounds the lower portion of the connecting rod 21. Thisconnecting rod is not longer of uniform diameter but contains a stopmeans 72. On each upward trip of hammer 14 the plate 70 strikes againstthe stop means 72 and imparts an upward axial force to this stop means,causing the valve element 2,0 to unseat from the lower seat 25 in anvil26. The total upward force exerted by piston 19 then causes the valveassembly to continue upward travel until the valve element 20 is seatedagainst the upper valve seat in annular member 24. One particularadvantage of such an arrangement is that it tends to insure that theunseating of the valve assembly from its lower seat occurs at the samepoint in each cycle of motion of the hammer 14.

If desired, a modification of FIGURE 8, shown in FIGURE 9, may beemployed. Here the upper annular valve member 32 is empjloyed as well asthe plate 70 associated with the stop means 72 on the connecting rod 21.The plate 70 is positioned on the bore of the hammer 14 at such a pointrelative to the top of the annular valve member 32 that plate 70dislodges the valve assembly just as the annular valve 3 2' minimizesflow through the passageway 41 outside tube 17 It is to be realized inseveral of the drawings, for simplicity only, a number of referencecharacters have been omitted. Those involving any difference inconstruction or operation have been particularly identified.

It is possible to modify the apparatus thus far discussed to providestill better for circulating a well as desired without affecting thedrilling system. Two versions of this are shown in FIGURES l0 and 11.The main modifications that have been made here consist of inserting astop 82 on the center tube at the lower end and below the side ports 36to prevent the piston 19 from passing through the bottom of the centertube 17. In FIGURE 10, center tube 17 is supported within the easing 11by a support which is attached, for example, by screw threads, to thecasing 11. It is desirable to introduce packing such as an O-ring 81 tominimize possibility of leaks of the drilling fluid used. I

Near the bottom of the center tube 17 a stop means 82 is employed, whichclosely surrounds the connecting rod 21 of the valve assembly andaccordingly guides it in its operation. The connecting rod 21 is hollow,thus providing fluid communication from the major part of the centertube 17 to the hollow bore 27 of anvil 26. The side ports 36 in thecenter tube 17 are located above the stop means 82 and are longeraxially than the axial thickness of piston 19, so that when piston 19 ispermitted to contact the stop means 82 the upper part of the side portsis above the piston 19.

Since the major part of the center tube 17 is in good fluidcommunication with the hollow bore 27 of anvil 26, i.e., the fluidexhaust from the drilling tool, the pressure in this major part of thecenter tube is considerably lower than that in the fluid intake 40 tothe tool.

The length of the piston rod is sochosen that under ordinary drillingconditions the piston 19 is at all times 11 above the side ports 36 sothat there is no fluid comnunication through passageway 41 into thehollow bore )f the connecting rod 21.

With this arrangement, the normal drilling operation of he tool shown inFIGURE 11 is as already discussed. [he tool in FIGURE is shown at aportion of the :ycle in which fluid pressure from passageway 41 on theower face of the hammer 14 is forcing the hammer upwardly, whilemaintaining the valve element in its lowermost position against thelower valve seat in rnvil 26. When the annular valve member 32approaches in lower outer edge of the center tube 17, fluid pressure 11the bore 35 decreases markedly while the upward pres- ;ure on the lowersurface of piston 19 is, if anything, ilightly increased, thus raisingthe valve assembly and Forcing it against the upper seat in annularmember 24, which completes the cutting off of fluid pressure from :hebottom face of the hammer 14. The hammer is now irged downward by thefluid pressure on its top surface, while the high pressure on the lowerface of piston 19 1nd the relatively low pressure on its upper face,still in luid communication with hollow bore 27, maintains the valveassembly in its uppermost position.

The impact of the hammer 14 on anvil 26 imparts a arge inertia force tothe valve assembly. This, and addizionally the force on the upper valveelement 20, impel :he valve assembly rapidly downward after the hammermpact to reseat it in the position shown in FIGURE 10.

However, during the time that the tool and bit are Off Jottom, anvil 26is in a much lower position. When the percussion drilling tool is oifbottom it is important to )e able to circulate drilling fluid throughthe tool and irill bit without the hammer operating. This is conven-.ently accomplished by providing the proper cooperation Jetween thevalve assembly and the anvil. When the tool 5 off bottom anvil 26 will,due to its weight, drop to he lower limits of its slidable positionwithin housing 11. Valve 20 is then seated in the seat within the anvil.The valve assembly is held seated by pressure in chamber 35 being largerthan the pressure in passageway 27. Hyiraulic forces on the hammer causeit to be driven upavardly until annular member 32 substantially engagesthe aottom end of center tube 17. Connecting rod 21 is constructed of alength such that the top of piston 19 is now )elow ports 36. Tube 21 ismade hollow as shown in FIGURE 11, for example. When piston 19 is belowport 26, there is relatively free flow from space of the in- :ake of thetool through the annular space between the iammer and center tube 17through ports 36 and hollow nterior of tube 21 to bore 27 of anvil 26.To start the 1001 all that is necessary to do is to continue tocirculate and lower the tool so that the bit rests on the bottom of :hehole. Continued lowering of the tool forces the anvil Z6 and the valve20 upwardly within the device so that .t will operate as describedpreviously.

It is not to be understood that the center tube 17 must be completelyremoved from fluid communication with he fluid intake 40 to the tool. Infact, in FIGURE 11, 1 small bore intake 83 is shown. This serves as ahydraulic resistance, permitting flow of extra fluid through he toolbeyond that required for the percussive drilling )peration but which maybe desirable for lifting of :uttings. The bore 83 must be maintained inonly limited :ommuication, so that the fluid pressure in the major partof the center tube, i.e., the part above piston 19 will be at aconsiderably lower pressure than that in :he fluid intake 40, althoughit will be somewhat above he pressure in hollow bore 27.

If there is no need for flow of extra actuating fluid :hrough the devicebeyond that used for percussive drill- .ng, the fluid communication withthe fluid intake 40 :o the device may be completely sealed off, forexample, Jy partition 84, as shown in FIGURE 12.

In FIGURES 10 and 11 we have also shown a par- :icularly advantageousshape for the valve element 20. The portion of maximum diameter has beenaxially extended to the order of one-quarter to one-half inch in length,and the recess 56 has been correspondingly deepened. Also, the uppervalve seat in annular member 24 has been moved upward axially to permitthe valve element 20 to enter the hammer 14 so that impact of the hammeron the anvil occurs before valve element 20 enters the recess 56.Increasing the axial length of the portion of the valve element 20 ofmaximum diameter means that the clearance between the valve element andrecess 56 can be increased considerably with negligible effect on thevalve action. Increased clearance means that there is much less erosionof the outer valve surface by the drilling fluid.

In FIGURE 11 the annular member 24 is shown held in place by a threadedannular ring 85, though other stop arrangements could be employed.Preferably, an O-ring type seal or packing 86 is employed between thevalve connecting rod 21 and the stop means 82.

It is apparent that certain features are essential to this design andothers can be considerably varied. In

all cases there is a center tube with a close fitting piston I inside,the upper surface of the piston being exposed to a pressure considerablylower than that at the fluid intake to the tool while the lower surfaceis exposed to the higher operating pressure of the actuating liquid.There is a stepped piston with pressure always being exerted against itsupper, smaller face and periodically exerting against its lower, largerface to cause it to reciprocate. There is a valve assembly whichincludes the piston and which is aligned with the center tube, all beingwithin the hammer. The valve assembly includes a double-acting valvewhich seats alternately in the top of the anvil and the lower part ofthe hammer. There is a means for unseating the valve from its lowermostposition only after the hammer has reached substantially the upper endof its stroke. There is a system for preventing the valve in itsuppermost position from seating in the lower position until after thehammer has impacted against the anvil. Since numerous variations havebeen shown, and still others are apparent to those skilled in this art,the invention is best described by the appended claims.

What is claimed is:

1. A vibratory drilling device comprising:

a housing having a port in the wall thereof,

a hollow cylindrical hammer reciprocally mounted within said housing,

sealing means between said hammer and said housing and cooperatingtherewith to form a variable volume chamber therebetween adjacent and influid communication with said port, the reciprocating of said hammervarying the volume of said variable volume chamber,

a central tube substantially concentrically mounted within andstationary with respect to said housing, the outer diameter of said tubebeing generally smaller than the inner diameter of said hammer,

a valve assembly including a cylindrical valve element and a pistonfitting the inside of said tube, said valve element and said pistonbeing connected a fixed distance apart by a connecting member,

a first annular member carried by said hammer above the bottom thereofso shaped and cooperating with said valve assembly as to cause asubstantial upward force to said valve assembly each upward stroke ofsaid hammer sufficient to unseat said valve assembly, a second annularmember carried by said hammer below said first annular member but nearthe bottom of said hammer to form a seat for the upper side of saidvalveelement, and

a hollow cylindrical anvil slidably fixed within and fitting the lowerportion of said casing with the top thereof below the bottom of saidhammer, said anvil being so shaped relative to said housing as totransmit axial torque, the bottom of said anvil being shaped forcoupling to a drill bit, the hollow part 13 of said anvil being shapedadjacent the top to form a seat for the lower side of said valveelement, the sealing area of said seat having a diameter which exceedsthe diameter of said piston.

2. Apparatus in accordance with claim 1 in which one of the bottom ofsaid hammer and the top of said anvil is provided with drainage groovesconnecting the outer part thereof with the hollow central portionthereof.

3. Apparatus according to claim 1 in which the least inside diameter ofsaid second annular member is less than the diameter of said piston.

4. Apparatus according to claim 1 in which the least diameter of saidseat of said anvil exceeds the diameter of said piston.

5. Apparatus in accordance with claim 1 including:

(1) stop means on said valve assembly, and

(2) impact means fixed to said hammer and axially aligned with said stopmeans in such position that said impact means imparts an upward axialforce to said stop means (and hence to said valve assembly) each strokeof said hammer at least near the upper end of motion of said hammer, tounseat said valve assembly from its lowermost position.

6. Apparatus according to claim 4 including means surrounding saidconnecting member and below any side port in said center tube forpreventing flow of fluid through the bottom of said tube when saidhammer is near the upper end of its movement.

7. Apparatus according to claim 1 in which the upper part of said tubeis in fiuid communication with a zone of fluid pressure considerablylower than that present at the fluid intake to said device.

8. An apparatus in accordance with claim 1 in which the upper part ofsaid tube is connected to the outside of said casing and in which one ofthe bottom of said harnmer and the top of said anvil is provided withdrainage grooves connecting the outer part thereof with the hollowcentral portion of the anvil.

9. Apparatus in accordance with claim 1 in which said second annularmember is slidably fixed within said hammer, so that initial contact ofthe upper surface of said valve element with said second annular memberis damped by motion of said second annular member with respect to saidhammer.

10. Apparatus in accordance with claim 1 in which the inertial force ofsaid valve assembly upon impact of 'said hammer on said anvil is a majorforce moving said valve assembly from its maximumupward to maximum downward position relative to said hammer.

11. A fluid actuated percussion drilling tool comprismg:

(l) a tubular casing containing an upper portion of smaller insidediameter than that of the lower portion thereof, there being a portthrough the wall of said casing below but near the junction of saidupper and said lower portion,

(2) a center tube substantially concentrically mounted within and onsaid casing with at least part thereof extending down into the lowerportion of said casing, the upper part of said tube being connected tothe outside of said casing, said tube containing a side port near thelower end thereof,

(3) a valve assembly including a cylindrical valve element and a pistonfitting the inside of said tube, said valve element and said pistonbeing connected a fixed distance apart by a connecting rod,

(4) a hollow, stepped cylindrical hammer slidably mounted within saidcasing and around said tube with upper outer diameter fitting the upperportion of said casing and lower outer diameter fitting the lowerportion of said casing, the inner diameter of said hammer generallyexceeding the outer diamter of said tube, said hammer carrying above thebottom thereof an annular member shaped to slidably fit said tube andadapted to reduce fluid com- 14 munication between said tube below saidpiston and the bottom of said hammer when said annular member fits saidtube, said hammer additionally carrying below said annular member asecond annular member above but near the bottom of said hammer, theleast inside diameter of which is less than the diameter of said piston,and which is adapted to form a seat for the upper side of said valveelement, (5) means surrounding said rod and below any side port in saidtube for preventing flow of fluid through the bottom of said tube whensaid hammer is near the upper end of its movement, and

(6) a hollow cylindrical anvil slidably constrained within and fittingthe lower portion of said casing in splined relation thereto, with thetop of said anvil below the bottom of said hammer, the bottom of saidanvil being shaped for coupling to a drill bit, said anvil being shapedadjacent the top to form a seat for the lower side of said valveelement, the maximum diameter of the sealing area of said seat exceedingthe diameter of said piston.

12. Apparatus in accordance with claim 11 in which said means forpreventing flow of fluid through the bottom of said tube comprises apartition closely fitting said rod and said tube and attached to one ofsaid tube and said hammer and in which a passageway is provided Withinsaid anvil establishing fluid communication between the top and the borethereof below said seat.

13. Apparatus in accordance with claim 12 in which said seat for saidvalve element in the top of said anvil is recessed below the top of saidanvil and said anvil is shaped above said seat to accommodate themaximum diameter of said valve element, so that on each down stroke ofsaid hammer said anvil is struck by said hammer before said valveelement seats in said anvil.

14. A liquid actuated percussion drilling tool compris- (l) a hollowcylindrical casing having an upper portion of smaller internal diameterthan that of the lower portion and at least one radial port in saidlower portion adjacent said upper portion,

(2) a hollow cylindrical anvil slidably constrained and closely fittingthe lower portion of said casing in splined relation thereto, said anvilbeing shaped at the lower end for connection to a drill bit, and beingshaped at the top of the hollow portion to define a recessed valve seat,

(3) a right cylindrical tube concentrically mounted within and on saidupper portion of said casing and connected to the outside of saidcasing, the maximum diameter of the sealing area of said seat exceedingthe inside diameter of said tube, said tube containing a radial portadjacent the lower end thereof,

(4) a valve assembly including a cylindrical valve element attachedthrough a valve rod to a piston slidably close fitting within said tubeabove said radial port, the lower surface of said element aligned andmating with said valve seat and fitting Within the recess above saidseat,

(5) a cylindrical hollow hammer having an upper portion slidably closefitting the upper portion of said casing and a lower portion slidablyclose fitting the lower portion of said casing, the major part of thehollow portion of said hammer being larger than the outside diameter ofsaid tube, said hammer carrying an annular valving element closelyfitting the lower end of said tube and adapted to restrict liquidpassage through the annular passage between said tube and said hammerwhen said valving element approaches the lower part of said tube, saidhammer also carrying below said valving element and slidablyconstraining an upper valve seat member aligned and mating with theupper surface of said valve element,

(6) means mounted on one of said tube and said hammet for sealingbetween said tube and said rod at least during the upper part of thestroke of said hammer.

15. An apparatus according to claim 14 in which at least one of theadjacent surfaces of said hammer and said anvil is radially grooved todrain fluid from between said surfaces into the hollow portion of saidanvil prior to impact of said hammer on said anvil.

16 A vibratory drilling device comprising:

a housing having a port in the wall thereof,

a hollow cylindrical hammer reciprocally mounted within said housing,

sealing means between said hammer and said housing and cooperatingtherewith to form a variable volume chamber therebetween adjacent and influid communication with said port, the reciprocating of said hammervarying the volume of said variable volume chamber,

a central tube substantially concentrically mounted within andstationary with respect to said housing, the outer diameter of said tubebeing generally smaller than the inner diameter of said hammer, a lowpressure portion of said tube above its lower end being in fluidcommunication with a zone of fluid pressure considerably lower than thatpresent at the fluid intake to said device, said tube containing a portnear the lower end thereof,

a valve assembly including a piston slidably fitting the inside of saidtube and a valve element exterior of the lower end of said tube, saidvalve element and said piston being connected a fixed distance apart bya hollow connecting rod, the upper side of said piston being incommunication with said low pressure portion of said tube,

a first annular member carried by said hammer above the bottom thereofand shaped to slidably fit said tube and adapted to reduce fluidcommunication between the annular space between said tube and saidhammer and the bottom of said hammer when said annular member is movedto an upper position to fit about said tube,

a second annular member carried by said hammer above but near the bottomof said hammer, the least inside diameter of said second annular memberbeing less than the diameter of said piston, said second annular memberbeing further adapted to form a seat for the upper side of said valveelement,

means surrounding said connecting rod and below said side port in saidtube for preventing flow of fluid through the bottom of said tube,

hollow cylindrical anvil slidably constrained within and fitting thelower portion of said casing, said anvil being so shaped relative tosaid housing as to transmit axial torque, the bottom of said anvil beingshaped for coupling to a drill bit, the hollow part of said anvil beingshaped adjacent the top to form a seat with a lower side of said valveelement, the seating area of said seat in said anvil having a diameterwhich exceeds the diameter of said piston.

17. Apparatus according to claim 16 in which said seat for said valveelement in the top of said anvil is recessed below the top of said anviland said anvil is shaped above said seat to accommodate the maximumdiameter of said valve element so that on each down stroke of saidhammer said anvil is struck by said hammer before said valve elementseats in said anvil, and

said center tube is in limited fluid communication with said fluidintake to said device but the fluid pressure in the major part of saidcenter tube is considerably lower than that in said fluid intake.

18. Apparatus as defined in claim 16 in which the structuralrelationship is such that when said anvil is in its lowermost positionin said housing and in which said valve element of said valve assemblyis seated in the seat of said anvil, the said piston is below the portin the wall 16 of said center tube so that there is relatively freefluid communication and flow from the annulus between said hammer andsaid center tube through said port in said center tube, the hollowportion of said connecting rod and the hollow bore of said anvil.

19. In a percussion drill having a casing with a forward part of greatertransverse area than the rear part thereof, a hammer piston reciprocablein said casing and having differential forward and rearward workingfaces received respectively in said casing forward and rear parts, therebeing a longitudinal passage extending through said piston, a connectionfor supplying operating fluid to said casing rear part under normaloperating conditions, and an anvil in said casing forward part with anexhaust duct therethrough, the improvement comprising first and secondopposing value seats respectively at the adjacent ends of saidlongitudinal passage and said exhaust duct, a check valve receivedbetween said seats, and means operable on said valve for impelling thesame towards said first seat, under normal operating conditions, duringthe latter part of the rearward return stroke of said piston forrestricting said piston passage and exhausting said casing forward partthrough said anvil duct and thereby initiating the forward power stroke,said valve impelling means being calibrated and said valve being ofsufiicient mass to cause said valve to be impelled forwardly againstsaid anvil seat, \upon striking of the anvil by said piston, to clearsaid piston passage and close said exhaust duct and thereby initiate thereturn stroke of the piston.

20. In a fluid operated percussion drill, a casing, an anvil at theforward end of said casing having an exhaust duct, a piston reciprocablein said casing for beating upon said anvil, said piston having alongitudinal passage therethrough and having a forward working facewhich is larger than the rearward working face thereof, and a connectionat the rear end of said casing for constantly supplying operating fluidto said piston rear face and forwardly through said piston passage undernormal operating conditions, the improvement comprising opposing pistonand anvil valve seats at the adjacent ends of said piston passage andsaid exhaust duct, a: double acting check valve having seating partsmovable between and cooperable with said seats, and means for impellingsaid valve toward said piston valve seat under normal operatingconditions during the latter part of the rearward return stroke of saidpiston while opening said exhaust duct to said casing forward part forproducing the forward power stroke of said piston, said valve seatsbeing spaced apart axially of the drill a greater distance than saidseating parts and said valve impelling means being calibrated and saidvalve being constructed and arranged to cause said piston to be impelledagainst said anvil seat, when said piston strikes said anvil, to closesaid exhaust duct and open said piston passage to said casing forwardpart and thereby produce the return stroke of said piston.

21. In a percussion drill having a casing, a connection for supplyingoperating fluid to the rearward part of said casing and an anvil at theforward part thereof, a hammer piston reciprocable in said casing tobeat upon said anvil, the forwardly-facing area of said piston beingexposed to the forward part of said casing and being greater than therearwardly-facing area thereof, passage means leading from saidconnection to the forward part of said casing, an exhaust duct leadingfrom said casing forward part, the improvement comprising valve seatelements, respectively, in the outlet of said passage means and theinlet of said duct, valve means movable between said seat elements, andmeans for alternately causing seating ofsaid valve means on said exhaustduct and passage means seat elements to thereby cause successiveapplication of the operating fluid pressure through said passage seatelement to said piston forwardly-facing area, while said exhaust ductseating element is closed, for impelling piston area while exhaustingsaid forward casing part through said exhaust duct seat element to causesaid piston to beat upon said anvil.

22. In a fluid operated percussion tool, a casing, an anvil at theforward part of said casing with an exhaust duct, a diflerential pistonworking in said casing with its forward working face larger intransverse area than its rearward working face, a connection at the rearend of said casing for supplying working fluid to the rearward part ofsaid casing, and a longitudinal passage through said piston, theimprovement comprising opposing piston and anvil valve seats,respectively, at the adjacent ends of said piston passage and anvilduct, a unitary doubleacting check valve floating between said seats,and means to maintain said valve against said piston seat during normaloperation in the latter part of the rearward return stroke and duringthe forward working stroke of said piston to cause said working stroke,said valve maintaining means being calibrated and said valve beingconstructed and arranged to cause said valve to be impelled forwardly byinertia upon striking of said anvil by said piston to close said anvilexhaust duct and again expose said larger piston forward surface to theworking fluid to repeat the cycle.

23. A percussion drill as described in claim: 22 in which said valvemeans comprises a one-piece valve body having upper and lower seatingfaces for cooperating alternately with said seating elements.

24. A percussion drill as described in claim 23 further includingcooperating structures projecting, respectively, from said valve bodyand the wall of said piston passage for unseating said valve body fromsaid exhaust duct seat element during the return stroke of said piston.

25. A percussion drill as described in claim 22 in which said pistonvalve seat constitutes a substantial restriction in said piston passageto reduce the area of said valve exposed to the operating fluid duringthe working stroke and thereby reduce the force necessary to maintainsaid valve on 'said piston seat during the working stroke.

26. A percussion drill as described in claim 25 in which said passagevalve seat is separately formed and replaceable for repair purposes andto adjust the area of said valve means exposed to the operating fluidpressure when said valve means is seated on said passage seat element.

27. A percussion drill as described in claim 22 further including a stopmember in the rear part of said casing positioned to limit rearwardmovement of said piston but to clear said piston during normalreciprocation thereof.

28. A drill as described in claim 22 further including a constantly openbypass opening through said valve body.

29. In a percussion drill having a casing with an upper part of greatertransverse area than the lower part thereof, a hollow hammerreciprocable in said casing between a lower and an upper position andhaving differential upper and lower working faces received respectivelyin said casing upper and lower parts, a connection for supplyingoperating fluids to said casing upper part under normal operatingconditions and an anvil in said casing lower part with an exhaust ducttherethrough, the improvement comprising:

a center guide tube supported from the upper part of said casing andextending down into the hollow interior of said hammer, there being anannular space between said hammer and said center guide tube for theflow of fluid therethrough;

an anvil valve seat in the upper part of said anvil surrounding saidduct;

a hammer valve seat carried in the lower portion of said hammer;

a valve means having a lower surface and an upper surface for seatingalternatively respectively in 'said anvil seat and said hammer seat;

an annular member carried by said hammer and shaped to slideably fit thelower outer wall of said center tube when said hammer is in an upperposition so as to reduce the flow of fluid through said annular space;

means to move said valve upwardly toward said ham mer valve seat whensaid hammer is in its upper position.

30. A percussion drill as defined in claim 29 including a passage meansfrom said connection through said center tube and said valve element tosaid exhaust duct.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 745,900 12/1903 Payton 91--225 2,758,817 8/1956Bassinger 91- 50 2,947,519 8/1960 Fencht 173-73 3,167,136 1/1965 Cook173-80 3,180,434 4/1965 Vincent 173-'73 3, 195,657 7/ 1965 Collier1173-66 NI LE C. BY-ERS, JR., Primary Examiner U.S. Cl. X.R.

